Several advanced flow monitoring solutions have been invented over the years:
One such approach (Miller, Jr. et al., U.S. Pat. No. 4,532,811) applies a thermal pulse to a stream of fluid and has a single downstream heat sensor to sense the thermal pulse. The transit time between the heating element and the heat sensor determines flow velocity. The Miller thermal pulse technique is effective over a wide range of fluid temperatures, because the unheated fluid is used as a reference: the downstream sensor detects thermal pulses, i.e. envelopes of fluid traveling through the flight conduit that are warmer than the unheated fluid. Therefore, the thermal pulse technique is advantageously insensitive to changes in ambient temperature.
Jerman, et al., U.S. Pat. No. 5,533,412 present an improvement to Miller's approach by providing at least two spaced apart sensors located along the flight conduit downstream from the thermal marking position and the flow velocity is derived from the time it takes the pulse to travel between two sensors.
Mosier, et. al., U.S. Pat. No. 6,660,675, and continuation in part Harnett, U.S. Pat. No. 7,225,683, disclose a device for measuring fluid flow rates over a wide range which operates by marking the fluid by producing compositional variations in the fluid (pulses), that are subsequently detected downstream from the marking position to derive a flow rate. Each pulse, comprising a small fluid volume, whose composition is different from the mean composition of the fluid, can be created by electrochemical means, such as by electrolysis of a solvent, electrolysis of a dissolved species, or electrodialysis of a dissolved ionic species. Measurements of the conductivity of the fluid can be used to detect the arrival time of the pulses, from which the fluid flow rate can be determined. A pair of spaced apart electrodes can be used to produce the electrochemical pulse mark.
To the knowledge of the inventor, none of the above inventions are believed to have resulted in practical commercial products, particularly for medical infusion where the medical tube sets are disposable, and integrating the above listed flow monitoring technologies in a disposable administration set is economically impractical.
U.S. Pat. No. 7,096,729 for Repko and al attempts to address the economical disadvantage of the above prior art by disclosing a disposable fluid flow sensor, which generally includes a flow channel assembly comprising a flow channel tube in association with a disposable flow channel portion. A sensor die is located proximate to a thin interface or membrane formed from the disposable flow channel portion, such that the sensor die measures a flow of fluid flowing through the flow channel tube and the disposable flow channel portion of the flow channel assembly. What Repko refers to to as a “disposable sensor” is actually a portion of a tube designed to externally receive a non-disposable sensor. In Repko's technology the sensor do not come in direct contact with the flow media (here after sometimes referred to as non-invasive vs. invasive) and therefore can introduce error due to a) variations in the flow conduit properties in particular those of the barrier (referred to as membrane in Repko's) between the sensor die and the flow media, b) variation in alignment between the flight tube and the sensor's die, c) user errors in replacing the sensor die appropriately and no means for detecting this error, and d) environmental effects such as dust or other contaminants, moisture and wetness, impressions of greasy fingers or talc from a nurse's gloves, e) loss of signal or information in the barrier (membrane) even at optimal operation conditions. Perhaps the most critical disadvantage of Repko's for critical flow measurement application such as medical infusion therapy is that an error or malfunction due to the above list of causes of errors can not be detected, and therefore can not be corrected for, while also can not alarm the medical staff.
Sage et al., U.S. Pat. No. 7,361,155 attempts to address some of the above disadvantages by disclosing a device that comprises a flow channel through which the liquid flows. During manufacture or at some other point prior to the delivery of the liquid, the flow channel is characterized in terms of one or more properties of flow of a liquid through the channel. This characterization is stored in such a way that the flow channel characterization is available to the liquid delivery device at time of use. At time of use, the liquid delivery system reads the stored flow channel characterization and uses the stored flow channel characterization for safe and accurate delivery of the liquid. While Sage' addresses the first disadvantage listed above for Repko's (marked as “a” in the previous paragraph) it fails to address the other disadvantages which are not related to manufacturing variations of the flow conduit. In particular Sage does not propose detecting and alarming for malfunction. More than anything, Sage's invention enlighten the problem need to be addressed to create an accurate and reliable device for measuring flows in disposable fluid transport systems which are economically practical. Sage's additional disadvantages is that calibrating each sensor, registering the calibration information on each individual sensor, and having delivery systems being equipped to read and process said registered information bare significant costs which are not desirable and usually not acceptable in medical care practices.
It is therefore the object to provide an economically practical flow measuring device for accurate and reliable flow monitoring in a fluid transport device.
It is another object to provide a flow measuring device that identifies human errors and malfunction and take measures to alarm a device or a person and to avoid harm or damage to a system, a patient, or a process or procedure.
It is another object to provide a flow measuring device that monitor flows in a fluid transport device in proximity to the outlet of said fluid transport device, and in particular where no possible disconnections may occur between the measuring position and the outlet of said fluid transport device.
It is another object to provide a flow measuring device that feedback to a flow control device which controls the flow in said fluid transport device, to improve the flow administration regime and to warn about hazardous conditions.
It is another object to associate a flow control device with the flow measuring device of the present invention.
It is another object of the present invention to provide safety means for preventing flow in the fluid transport device if the flow control device is suspected to malfunction.